The present invention relates to a display device and a driving method thereof for driving pixels by using a signal driver circuit provided with a memory, and in particular, to a liquid crystal display device and a driving method thereof for speeding up a response speed of liquid crystal for the purpose of improving the performance of displaying moving images.
In liquid crystal display devices, due to the slow response speed of liquid crystal, smearing and blurring occur in a display of moving images, and the quality of the displayed image is degraded. JP-A-4-288589 discloses a liquid crystal display device which speeds up the response speed of liquid crystal for the purpose of improving the quality of displayed images by eliminating occurrence of smearing and blurring in a display of moving images. In a case where frame-image signals are supplied to a liquid crystal display device successively in synchronism with a frame period of the liquid crystal display device from an external display signal source, the liquid crystal display device disclosed in JP-A-4-288589 is provided with a frame memory for storing image signals for an entire frame and a means for detecting time-varying changes between the frame-image signals stored in the frame memory and externally supplied frame-image signals. This liquid crystal display device corrects the supplied frame-image data so as to speed up the response speed by using an adaptive filter capable of varying its filter characteristics based upon the amount of the detected changes.
Recently there have been increasing opportunities for displaying moving images even on mobile equipment typified by mobile phones, since the mobile equipment can receive TV broadcasts now, for example. Therefore there has been a demand for improvement in moving-image displaying performance on small-sized liquid crystal display devices used for mobile phones. For the purpose of reducing power consumption by transferring video signals, liquid crystal display devices used for mobile phones employ a signal driver having a built-in frame memory capable of storing image signals for at least one frame. The signal source (a CPU, for example) which controls the liquid crystal display device does not transfer all the video signals for an entire frame at the changeover of images, but transfers to the signal driver, video signals associated only with pixels having undergone changes, and thereby changes image signals stored in the frame memory. The signal source reads out frame-image data from the frame memory in accordance with the frame frequency of the liquid crystal display device, and displays an image.
Generally, the frame rate of video signals transferred to the liquid crystal display device from the CPU is lower than the frame frequency (60 Hz, for example) of driving of the liquid crystal display, and therefore the liquid crystal display device displays the same frame image stored in the frame memory of the signal driver several times. In this case, in order to improve the quality of moving images displayed on the liquid crystal display devices used for mobile phones, the above-mentioned driving needs to be applied only to the first frame immediately after the changeover of images.
To correct video data for moving images, TV broadcasts and the like, JP-A-2002-132225 discloses a liquid crystal display device for improving gray scale displaying characteristics by correcting luminance signals and color-difference signals based upon features in an immediately preceding frame, and values of luminance signals and color-difference signals in the immediately preceding frame, by employing an image-quality correcting device comprised of a first signal converting means for converting supplied R, G and B signals into luminance and color-difference signals, a frame-feature extracting means for extracting features of luminance signals every frame, a signal correcting means for correcting luminance and color-difference signals, and a second signal converting means for luminance and color-difference signals outputted from the signal correcting means into R, G and B signals.